Amplifying circuit for micro-waves, especially millimeter waves



March 4, E958 AMPLIFYIN MAR E United States Patent AMPLIFYING CIRCUITFOR MICRO-WAVES, ESPECIALLY NHLLIMETER WAVES Georges Robert Pierre Mari,Paris, France Application December 14, 1954, Serial No. 475,078 Claimspriority, application France December 28, 1953 4 Claims. (Cl. 179171)The present invention relates to amplifying circuits for amplifyingmicro-wave signals, and more particularly to amplifiers for amplifyingsignals whose wave lengths are in the order of millimeters.

Briefiy, a circuit of the invention consists essentially of a rod offerrite, or of a dielectric material having a very high magneticpermeability. A D. C. magnetic field is directed along the axis of therod and the rod is situated along the axis of a cavity, cylindrical inshape, into which electromagnetic energy is injected in the form of a TMwave polarized circularly and having a frequency very definitely lowerthan that of the wave to be amplified. For instance if it is desired toamplify a Wave having a frequency of 50,000 mc./s. a frequency of theorder of 5,000 mc./s. will be taken as a frequency for the circularlypolarized wave.

The ultra high frequency wave to be amplified is propagated before andafter amplification, in circular coaxial guides, coaxial with theferrite rod, in the shape of a TE wave. The energy exchange is effectedthrough the medium of the motions in the direction of the spin ofelectrons. The circularly polarized wave with a relatively low frequencyimparts energy to the electrons located in the ferrite rod and thedirection of their spin has a precession motion accompanied by amutation motion imparted thereto. The ultra high frequency Wave isamplified by deriving energy from the mutation motion of the electrons.in the present specification and for greater convenience in expression,the wave having a relatively low frequency shall be called the supplywave.

The invention will be better understood from the detailed descriptionwhich will next be given in connection with the appended drawings,wherein:

Figure 1 represents a perspective view of an amplifier circuit inaccordance with the invention.

Figure 2 is a geometrical diagram utilized in explaining the operationof the circuit in Figure 1.

The amplifying circuit comprises a cylindrical cavity 2 along the axisof which a ferrite rod 3 is located. The cavity 2 is coupled with aninput circular guide 4 through which the energy to be amplified arrivesand with an output circular guide 5 through which the amplified energycomes out. The two guides 4 and 5 are coaxial with the cavity 2.

A permanent magnet, or an electromagnet, 6 makes it possible to apply aD. C. magnetic field H to the ferrite rod, parallel therewith. Thismagnet has the shape of a U and the two side branches of the U arepierced, near their ends, with two circular holes 7 and 8 which have thesame diameter as the guides 4 and 5 and which are extensions of thelatter. Inside the holes 7 and 8, radial fins are arranged, 9 and 10respectively, of ferromagnetic material, which, on the one hand, ensurethe continuity of the magnetic circuit and, on the other hand,constitute mode filters for the TE wave to be amplified.

In the cavity, the wave to be amplified is guided by the rod 3 (i. e.the" larger portion of its energy is localized in the rod and in theimmediate vicinity thereto) in the form of a magnetic field with anultra high frequency H located inside the rod and directed along itsaxis, and of an electric field in which the lines of force are circlesconcentric with the rod and the intensity of which decreases veryrapidly when the distance to the rod increases.

The cavity 2 is coupled, through a slot 11 with a rectangular guide 12,the axis of which is perpendicular to that of the cavity 2. This guideis energized by a micro-- wave oscillator tube 13 which generates thesupply wave with an angular frequency 9.

The cavity 2 is dimensioned so as to resonate with two i TM waves ofangular frequency 9 in the vicinity of the cut-off frequency of acircular wave guide having a diameter equal to that of the said cavity.The two TM waves have magnetic fields (considered at points of the Ozaxis of the cavity) of equal magnitudes, but perpendicular frequency ofthe cavity 2 is equal to 9, it is sufficient to introduce into thecavity energy with an angular frequency 9 through the slot 11 for thisenergy to be in the shape of a circularly polarized wave inside thecavity. The magnetic field l-l of this wave rotates with the angularfrequency 9 about the axis of the cavity 2.

The magnetizing of the ferrite is related to the orientation of theparticles, nuclei or electrons, having a magnetic moment M equal to oneor to an integral number of Bohrs magnetons, and a kinetic moment Iequal to A2 (h/21r), 11 being Plancks constant. 'The directions of themagnetic and kinetic moments of an electron are identical. Magnetism iscaused by unsaturated electron layers in which an electron remains inexcess, with its magnetic moment not compensated. Under the action ofso-called Weiss forces, allthe magnetic moments, not compensated, of theelectrons, have a tendency for being oriented parallel to one another.These Weiss forces found an explanation in wave mechanics and are aconsequence of Diracs electron spin theory.

The electron which has a very large kinetic moment with respect to thetorques applied thereto, reacts like a gyroscope. The energy is suppliedto the precession motion by the rotating magnetic field H of the waveshaving an angular frequency [2. The electromagnetic wave to beamplified, with an angular frequency w, is amplified at the expense ofthe mutation motion of the electron. Its magnetic field H verying at theangular frequency a; which is that of the nutation motion, the brakingof the mutation motion causes, by a gyroscopic effect, a varialocated inthe ferrite and the axis Oz is directed along the 7 common direction ofthe axis of the ferrite rod and of the D. C. magnetic field, H

If the electron is moving in any kind of motion, the calculations whichfollow are not affected since they consider only the motion about thecenter of gravity.

Let 0; be an axis directed along the strai'ghtline of Patented Mar. 4,1958 If, for a given direction of rotation of the electric field, theresonance angular intersection of the plane going through perpendicularto the common direction of the magneticv moment M and kinetic moment J,withtthe plane 0, any and O1; maxis in th ilat er Elena: t ri ht angle:w th he tt f- E V r" The field H rotating at angulanvelocitycauses. -nrcess o o =the dir bn the m ne i moment M z,--:S nee th e t om t c Waveto e amplified can exist 'in the cavity 2 onlyin; the shape TE i.. e.:has a magnetic field H which, alongfthe axis of the cavity ZTisdirected along s aid axis, only the variation oti angle q between theaxis-Ozand; the direction ofthe magnetic moment M is corrected'with thewave to he amplified, which makes it'ppssible to write t designata m-hw' a 1 1 j '0r=0 +'0 e1 (-1) (designating by 0 a complex quantity, themodulus and phase angle 'of'which are shown at the periodically varyingpart of angle 9).

'The' variation in nutati'on causes a variation in precession'and'one'may write, designating by 1,11 the precession angle (Fig. 2): V

and designating by 1/ thereal portion of b 'e (11 be ing acoinpleibquantity, the modulus and phase angletofv which are those ofthe periodically varying part'of 1,0).

The-components of the kinetic moment I and of the' magnetic moment MThecomponentsot the derivative of the kinetic moment with respect -totime t, for the kinetic moment are'in this" same trihedron= Thevariations in the direction of the magnetic moment have, asaconsequence; an energy radiation.

A portion of this energy isabsorbedby the atoms which constitute thecrystal lattice of. the fenitein le form of" thermal agitation.Thisenergy loss will-he neglected in what follows. I a l The otherportion is radiatedw outside the ferrite and constitutes theavailablevenergy. Since,. as-we saw, only the'variation of angle 0 iscoupled: with theradiation, the resulting braking torqueis directedalougOeand th valuef r will be'assigned to it, k being a constant and h lbeglplaee as a factor; for allowing later simplifications.

lumn g V r r 4: v r v In such conditions the resultingjol'fl ie of thetorques exerted can be written:

The derivativeof-thekinetic-momentisequal to the resultant moment-torthe torques WhiQh..giVegidentifying the components (5) with thecomponents (7), three equa-V tions, two of which are identical. v i VThe following system of 7 equations is thus obtained:

The system of'Equations'8 can be transfor-medgtaking the followingremarks into account:

The quotient of the moment of a torque by a ;kine tic;

moment has thedimensions of a frequency and we may 1 Further, H cos wtmay be considered as the real portionof H e The system of Equations 8then can he written; considering p and 0 as infinitely smallquantitiesoftthe first order and neglecting the second order'terms: 1

S2,,(cotan 00-:

zqele n l iul Writing-the equality of the coeflicients of e in' thesecond of Equations 11; we obtain:

'Equating; the constant terms. in we obtain:

cotan.0o=. WP (113) Finally, equating the'coetlicients of 2 inthefirstEquat on 11 e-obt in amplified. atvthe expenseot the kinetic energy ofthe.

. electrons should. he, propagated with a velocity closetto u sli htly sa r t an, t at or the. el ctrons, simila ly n heea eof hepr nt v i thamplifiedmave sbou clha e anane'nla tr uensy w cl set to butsl sh llSmaller ha then tu al nutat eni qu ney (lithe-Zeke n nsen e as-t otinuously brake? thisnuta ieasi fi automation, e ayeet the firstEquation. .11 V

In order to have a maximum coupling between the magnetic moment M andthe magnetic field H,,, 0 should be selected close to 90, i. e. sin 0close to unity. There results, then, from Equation 13, that $2 should beclose to 9, which, from Equation 9 gives the value of the D. C. field H(9 is assumed to be one of the data of the problem). The condition Thislatter condition (17) gives, from Equation the value of the rotatingfield H S having a very large value of the order, for instance of100,000 1r, Equation 10 also shows that H should be very large. As aresult, the cavity 2 should have a very large magnification factor forvoltage; to this effect, the ferrite, rod in which the losses occurshould have a very small diameter.

In the above calculations, the losses have been neglected. These lossesmake it necessary to supply, at the angular frequency 9 a much largerpower than that which the circuit makes it possible to obtain on theangular frequency w.

There will now be obvious to those skilled in the art many modificationsand variations utilizing the principles set forth and realizing many orall of the objects and advantages of the invention but which do notdepart essentially from the spirit of the invention.

What is claimed is: t

1. An amplifier for ultra-high frequency waves and operable in seriesbetween two cylindrical wave guides having a common axis and propagatingsaid waves according to the TE mode, comprising a cylindrical hollowresonator having its axis common with the axis of said guides andcoupled to said guides, said resonator including a rod of insulatingmaterial of very high magnetic permeability arranged along its axis,means for impressing upon said rod 21 direct-current magnetic fieldparallel to said axis and means for exciting in said resonator anauxiliary circularly polarised TM wave, the frequency of which is lowerthan the frequency of said Waves to be amplified, said insulatingmaterial being a ferromagnetic material characterized by a resonancefrequency and said resonator being tuned to the frequency of saidauxiliary wave, the latter frequency substantially coinciding with theferromagnetic resonance frequency of said material for a predeterminedrotational direction of said circularly polarized waves.

2. An amplifier as claimed in claim 1, wherein said material is aferromagnetic ferrite.

3. An amplifier as claimed in claim 1, wherein said auxiliary wave isapplied to said resonator by means of an auxiliary guide coupled tosaidresonator.

4. An amplifier as claimed in claim 1, wherein the frequency of saidauxiliary wave is about one-tenth of the frequency of the waves to beamplified.

References Cited in the file of this patent UNITED STATES PATENTS2,644,930 Luhrs et al. July 7, 1953 FOREIGN PATENTS 511,649 Belgium June14, 1952 OTHER REFERENCES Bell System Journal, vol. 31, pp. 22-26,January 1952.

